Colt 6700/6701

[Retired W4]

I ran into an AR that has me scratching my head and I was hoping someone could help me with it. It's a Competition HBAR with a very early CH number, shaved front sight similar to the 6724, and a muzzle brake firmly fixed to the threaded 20" C MP HBAR, 1 in 9, w/no bayo lug. It has a mark on the top right forward area of the upper that appears to be a C in a square (Colt proof).

So is it an R-6700, or an R-6701 Custom Shop gun? Help!

[Retired W4]

As Colt would sometimes do, it's a slick side lower with the pinned receiver block.